Studies on the biochemical and biological characterization of a new B-lymphotropic papovavirus (LPV) have continued during the past year. In biochemical studies of the viral genome, the origin of DNA replication was located. Using this as the reference point, we were able to align the genome of the virus to those of SV40 and BK virus based on data obtained by hybridization between specific fragments under low-stringency conditions. From the results of these experiments, the correlation between the physical and functional maps of the B-lymphotropic papovavirus genome was deduced. We were able to demonstrate transforming capacity of LPV using hamster embryo cells. Two months after exposure to LPV, foci of transformed cells appeared and the cells could thereafter be passaged indefinitely. Preliminary studies on the analysis of the transformed cells have shown that the cells contain intranuclear T-antigens which show some cross-reactivity with SV40, BK, and JC T-antibody. Analysis of the status of the viral genome in the transformed cells has revealed that most, if not all, of the viral DNA exists in a non-integrated, free state. Immunoprecipitation of transformed cell extracts with anti-LPV serum showed that the large T-antigen of LPV is an 84K protein, the same as that previously found in infected cells.